1. Field of the Invention
The present invention relates to assign channel distributing system and method for assigning radio channels optimally to a radio system in a system (wireless local loop) which uses a radio system comprising cellular telephones, etc. and contains general subscribers (telephones).
2. Description of the Related Art
An optimum arrangement of radio channels is an item indispensable to effectively use definite frequency resources.
As a channel arrangement system, there are known an interleave channel arrangement system or a split channel arrangement system, in which the center frequencies of respective channels are located between normal channel intervals. In these methods, it is impossible to use adjacent channels in the same cell because the spectra are overlapped between these channels. Further, even if use of adjacent cells is restricted, it suffers restriction due to interference conditions, and thus the drastic improvement of the use efficiency in frequency has not yet been achieved. However, it wold be possible to assign adjacent channels if the cells which use adjacent channels are separated from each other approximately the distance corresponding to the interval between second adjacent cells. In this case, however, the channel use efficiency is extremely lowered if the distribution is not uniform.
In order to solve these problems, there has been proposed a dynamic channel arrangement system for selecting channels which are within a fixed distance range from a cell and are not used in interference cells. However, this system has such a disadvantage that it is necessary to process information bridging over many base stations at high speed by a center station in conformity with the increase/reduction of traffic (an amount of information flowing per fixed time).
Further, there has been also proposed a distributed dynamic channel arrangement system in which each base station is provided with a priority function on channel use and the priority function is varied according to the magnitude of the interference level of each channel. However, this system has such a disadvantage that the interference relationship between the interference level measured by an individual base station and the interference level measured by other base stations is unclear and thus this system does not support timely traffic variation.
The above systems are described in more detail by Kuwahara in xe2x80x9c4.2.3 Channel Arrangement (pp132-136) of Chapter 4 of xe2x80x9cDIGITAL MOBILE COMMUNICATIONxe2x80x9d (Science Newspaper Co., Ltd.).
An object of the present invention is to provide an assign channel distributing system and method which can perform an optimum radio channel assignment to a radio system.
According to a first aspect of the present invention, there is provided an assign channel distributing system which comprises plural base stations which communicate with subscriber terminals, and a base station control-station for sending to the plural base stations information indicating whether each base station should serve as a master station or slave station (i.e., an assignment of a master station or a slave station to each of the base stations, and it is hereinafter referred to as xe2x80x9cmaster/slave assignment).
According to a second aspect of the present invention, there is provided an assign channel distributing method which comprises a first step of performing communications between a subscriber terminal and plural base stations, and a second step of sending to the plural base stations information indicating whether each base station serves as a master station or a slave station.
According to the assign channel distributing system and method of the present invention, on the basis of the information indicating the master/slave assignment which is sent from a base station control-station to the respective base stations, the information on the channel interference level, the desired channel number, and the like is exchanged between the master station and each slave station, whereby the master station performs the radio channel assignment on the slave stations on the basis of the information on the channel interference level, the desired channel number, and the like.